For example, charge coupled device (CCD) image sensors (CCD-type solid-state image pickup elements) or complementary metal oxide semiconductor (CMOS) image sensors (CMOS-type solid-state image pickup elements) have been known as solid-state image pickup elements. In addition, in recent years, the CMOS-type solid-state image pickup elements have attracted attention from the viewpoint of, for example, miniaturization and power consumption.
There is a CMOS image sensor including a digital circuit unit that performs, for example, processing of a video signal with digital processing and is mounted together with an analog circuit unit including a pixel array unit and an A/D converter, on the same chip (a semiconductor substrate). Mounting the digital circuit unit together with the analog circuit unit on the same chip in this manner causes digital noise arising from, for example, a variation in potential between a power source and a ground in the circuit operation of the digital circuit unit. The noise exerts an adverse effect on the circuit operation of the analog circuit unit, resulting in degradation in image quality.
In order to avoid the degradation in image quality arising from the digital noise, conventionally, increasing the speed of a clock pulse in signal processing by the digital circuit unit, causes the digital circuit unit to perform the signal processing during a horizontal blanking period during which signal reading from a pixel is not performed (e.g., refer to Patent Document 1). In addition, for a configuration including the digital circuit unit and the analog circuit unit not mounted together on the same chip, the digital circuit unit artificially starts to operate before the analog circuit unit starts to operate, in order to avoid the degradation in image quality arising from the digital noise (e.g., refer to Patent Document 2).